A fuel cell is a device for directly converting the chemical energy of the fuel into electrical Power. A fuel cell comprises an anode, a cathode, and an electrolyte disposed between the two electrodes.
In the operation of a typical fuel cell, fuel gas is fed to a porous anode and an oxidant gas is fed to a porous cathode. The reactant gases diffuse through the electrodes and electrochemically react to yield water, heat, and electrical energy. At the anode, the fuel gives up electrons in an electrochemical oxidation reaction. The electrical current so generated is conducted from the anode through an external circuit to the cathode. At the cathode, the electrons are electrochemically combined with the oxidant. A flow of ions through the electrolyte completes the circuit.
Fuel cells may be categorized according to the type of electrolyte used. Four types of fuel cells are generally considered to be in the mainstream of the technology: alkaline fuel cells, acid fuel cells, molten carbonate fuel cells and solid electrolyte fuel cells.
Solid electrolyte fuel cells operate at high temperature and allow direct consumption of hydrocarbon fuels to provide a high power density. Solid electrolyte fuel cells also eliminate liquid electrolyte containment problems.
The use of ceria compositions as the electrolyte in solid electrolyte fuel cells is known, see, e.g., Tuller, H.L. and Nowick, A.S., "Doped Ceria as a Solid Oxide Electrolyte", Journal of the Electrochemical Society: Solid-State Science, Volume 122, No. 2,225 (February 1975). A ceria electrolyte offers a high ionic conductivity at temperatures in the range of 600 to 1000.degree. C. However, in a reducing atmosphere such as that encountered on the hydrogen electrode side of the electrolyte, a conventional ceria electrolyte becomes an electronic as well as an ionic conductor, and allows short circuiting across the electrolyte. The short circuiting reduces the performance of the fuel cell.
What is needed in the art is a way to eliminate or reduce these losses so that ceria electrolyte compositions may find practical application in fuel cell power plants.